The present invention relates to a method for manufacturing a magnetic head by a thin-film technique, which head comprises a magnetic conduction body for carrying magnetic flux and which is similar to a ring head having at least two magnet legs which define an enlarged space through which the turns of at least one write and/or read coil winding extend and which have pole surfaces facing a recording medium disposed in a common plane having a predetermined small spacing from each other, in which method
a preliminary product of the magnetic head is formed on a substrate body, the magnet legs of which extend beyond the plane of the pole surfaces and there form end pieces which are spaced by only a small gap and which are worked off by material-removing machining of the substrate body from the side facing the recording medium up to the plane of the pole surfaces,
a conductor structure of electrically conducting material is furthermore applied to the substrate body in such a manner that this structure is separated, just when the plane of the pole surfaces is reached in the material-removing machining of the substrate body, into two conductor parts electrically insulated from each other, and
the electric resistance between these conductor parts is utilized for controlling the material-removing machining. Such a method is known, for instance, from DE-OS No. 33 33 590.
With this known method, magnetic heads for longitudinal (horizontal) as well as for perpendicular (vertical) magnetization of corresponding recording media can be produced. The principles of these types of magnetization for the storage of information are discussed, for instance, in the publication "IEEE Transactions on Magnetics", vol. MAG-16, no. 1, January 1980, pages 71 to 76. Magnetic heads known per se which can be used for these types of magnetization can comprise, in particular, a conducting body for carrying the magnetic flux, designed similar to a ring head and having at least two magnet legs of high-permeability material. These magnet legs define a space which is enlarged due to an increase of their mutual spacing, through which the turns of at least one write and/or read coil winding extend and develop, on the side facing the recording medium, magnet poles which are arranged one behind the other with a predetermined small spacing. The surface of these poles facing the recording medium should come to lie in a common plane which extends at least approximately parallel to the surface of the recording medium.
The exact design of such magnet legs, however, encounters difficulties in magnetic heads which are to be produced by a thin-film technique (see the DE-OS cited above). One is therefore compelled to develop on a nonmagnetic substrate body, first, a preliminary product of at least one magnetic head in such a way that the magnet legs are extended beyond the plane of the pole pieces in the direction toward the recording medimm. In this extended region, the magnet legs form essentially parallel extending end pieces which are spaced only by a narrow gap which is also called the air gap. On the substrate body, an auxiliary structure of electrically conducting nonmagnetic material must be formed which represents a conductor structure or loop, with the aid of which the removal of material of the substrate body of the at least one magnetic head from the side facing the recording medium can be assured up to the plane in which the surfaces of the poles of the magnet leg of the magnetic head are to lie.
Accordingly, one conductor structure called a guiding mark or a machining sensor or feeler is applied, in the known method, to the flat side carrying the magnetic head, of a substrate body on both sides of the head. For forming these structures, an electrically conducting base surface is deposited first which covers zones to both sides of the measuring line which is defined by a plane in which the pole surfaces of the magnet leg to be formed are to extend. This base surface is then coated partially with a barrier surface of insulating material, wherein this barrier surface extends from above exactly to the measuring line fixed by the plane. Above this barrier surface protrudes from below, in finger-fashion, a further electrically conducting conductor surface which is connected to the region of the base surface which is exposed below the mentioned line and is not covered by the barrier surface, in an electrically conducting manner. If now the substrate body is ground off from its underside facing the recording medium by a material-removing process such as lapping or another kind of precision machining, the electrical contact between the finger-shaped conductor surface and the base surface of the conductor structure is eliminated when the measuring line is reached. The change in resistance between these two conductor parts connected therewith can then be utilized as a control signal for stopping the material-removing processing.
In this known method, the pole height, i.e., the vertical extent of the pole zone, in which the end pieces of the two magnet legs are parallel to each other, and thereby the desired position of the pole surfaces of the magnet legs, can be adjusted only indirectly by means of conductor structures representing auxiliary designs. An appropriate control of the material-removing processing of the substrate body and thereby, of the magnet legs in their pole zone, however, is rather costly, and a relatively large portion of the area is occupied by the auxiliary design on the substrate body. As a result, the number of magnetic heads which can be deposited simultaneously side by side on an available area of a substrate body is reduced accordingly.